1. Field of the Invention
This invention relates generally to a system and method of in-season nitrogen measurement and fertilization of non-leguminous crops from digital image analysis, and more particularly to a system and method of measuring leaf nitrogen concentration using dark green color index values from a digital image of a non-legume crop and determining the amount of in-season nitrogen fertilization to be applied to maximize crop yield potential.
2. Description of the Related Art
Management of fertilizer nitrogen is a critical component for producing consistent crop yields. Nitrogen fertilizer also represents a considerable input cost and has serious environmental consequences if over applied. The prevalence of nitrogen in the cells of agronomic crops means that harvest removes large quantities of nitrogen from a field, and, in doing so, creates of a paucity of the nutrient residual in the soil for future production. This, coupled with nitrogen loss from soils by leaching, volatilization and denitrification, establishes a situation in which nitrogen is the nutritional factor most commonly limiting crop yield potential. To remedy this, plant-available nitrogen forms are provided to the crop in the form of chemical fertilizers, such as anhydrous ammonia and urea. Synthetic nitrogen fertilization is a cornerstone of modern agriculture because it provides the nutrients needed for elevated grain yield and quality. Therefore, it is important to apply the correct amount of fertilizer to meet the crop's need but not to supply more than is required because of the cost and environmental concerns.
The diagnosis of in-season nitrogen deficiencies must be followed by corrective nitrogen applications to recover potential yield. A key to corrective nitrogen fertilization action is up-to-date knowledge of advent and degree of nitrogen deficiency. Immediate knowledge of plant nitrogen concentration is often not obtainable due to a lag time for processing. This lag time can negatively affect the value of the derived information due to the short window during which nitrogen demand is increasing and deficiencies can be most effectively corrected. Nitrogen requirements of the crop increase dramatically beginning with the V6 development stage, and the final chance for practical application of non-foliar nitrogen fertilization (due to increasing plant height) occurs about a week later at the V8 stage. The V8 development stage is also the final point at which corrective applications can re-establish near complete yield potential.
In addition to timing, spatial variability exists within any field relative to the amount of nitrogen required by a particular crop. An attempt to reduce nitrogen fertilizer losses must take this into account. A field-wide map for variable-rate nitrogen application can be achieved several ways, but must have as high a level of accuracy and resolution as possible to maximize fertilizer efficiency.
There are few tools that are currently available to help farmers determine if crop nitrogen levels during the season are adequate, and several techniques have been used to objectively measure crop color, including reflectance measurements, chlorophyll and amino acid analysis, and comparison with standardized colors. All of these techniques have certain disadvantages compared with subjective color ratings. Reflectance, chlorophyll, and amino acid measurements all require relatively expensive equipment, and transport of samples to a laboratory for analysis. Shipping these measurements to a qualified testing service can compromise the brief window in which the information might be of value. In addition, correlations between color and chlorophyll or amino acid measurements are either species or cultivar dependent. A hand-held SPAD meter (Minolta) gives real-time chlorophyll concentration of leaves in the field, and chlorophyll concentration has a close relationship to leaf nitrogen concentration. Disadvantages of the SPAD meter include a large initial equipment cost and that a large number of measurements may be required to make a representative measurement.
Digital image analysis is an emerging method of nitrogen status diagnosis that addresses the needs of time, cost, and data resolution. Through digital photography, farmers can instantaneously obtain millions of bits of information on a relatively large crop canopy. For example, a digital image taken of a crop using a 1280×960 pixel resolution contains 1,228,800 pixels, with each pixel containing independent color information about the crop.
The information contained in each digital image includes the amount of red, green and blue (“RGB”) light emitted for each pixel in the digital image. Although it may be intuitive to use the green levels of the RGB information to quantify the green color of the digital image, the intensity of red and blue will confound how green the digital image appears. To ease the interpretation of digital color data, RGB values can be converted directly to hue, saturation and brightness (“HSB”) values that are based on human perception of color. In HSB color description, hue is defined as an angle on a continuous circular scale from 0° to 360° (0°=red, 60°=yellow, 120°=green, 180°=cyan, 240°=blue, 300°=magenta), saturation is the purity of the color from 0% (gray) to 100% (fully saturated color), and brightness is the relative lightness or darkness of the color from 0% (black) to 100% (white).
It is therefore desirable to provide a system and method of determining nitrogen levels from a digital image and in-season nitrogen measurement and fertilization of non-leguminous crops from digital image analysis that does not require specialized, expensive equipment.
It is further desirable to provide the systems and methods disclosed herein that can easily be sent electronically, such as via email or to a web-based server, for immediate analysis.
It is still further desirable to the systems and methods disclosed herein that integrate values over a much larger leaf sample than does the SPAD meter.
It is yet further desirable to provide the systems and methods disclosed herein that do not rely on chemical processes of measuring leaf nitrogen.
It is yet further desirable to provide the systems and methods disclosed herein having quick turn-around times to provide farmers with real-time nitrogen concentration and yield information for the crop.
It is still yet further desirable to provide the systems and methods disclosed herein that provide early, precise and accurate measurements of current nitrogen status crucial for maintaining high nitrogen use efficiencies in the crop.
It is still yet further desirable to provide the systems and methods disclosed herein that provide favorable nutrient conditions for maximizing potential yield of the crop.
It is still further desirable to provide the systems and methods disclosed herein that employ DGCI as a means of correcting nitrogen deficiencies in the crop at specific development stages.
It is yet further desirable to provide the systems and methods disclosed herein that improve nitrogen-use efficiency, thereby benefiting farmers, crop producers and consumers with lower costs of production, less environmental pollutants, and greater energy efficiency.